* Asian stock markets : https://tmsnrt.rs/2zpUAr4* MSCI ex-Japan off 0.4%, Australia and South Korea down 0.9% each* E-Minis for S&P500 fall 0.2%* U.S. Treasury yields at the lowest since September 2017By Swati PandeySYDNEY, May 29 (Reuters) - Asian shares stumbled on Wednesday and global bonds rallied as investors fretted over the outlook for world growth with trade tensions between Washington an